JP2000241861A - Stroboscopic received light quantity digitizing circuit and stroboscopic emitted light quantity control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a discharging time and a discharged accumulated quantity accurately proportional to each other and to largely improve a stroboscopic emitted light quantity, namely, a measurement accuracy of a photo-electric current by that a fixed quantity discharging means is always synchronized with a prescribed sampling frequency, and also discharging a fixed accumulated quantity for a fixed period shorter than a sampling cycle. SOLUTION: A photo-electric current from a photo-diode PD charges a capacitor Cpd, and when the potential exceeds (Vcc-Vth), an output of a comparator CMP becomes Hi. The comparator output Hi is latched by a D-type flip-plop FF at the rising of a sample clock CK, and a constant current source CSI becomes active in the half cycle of the following Lo of the sample clock CK. The capacitor Cpd discharges a certain quantity of charges for this period, and the potential of the capacitor Cpd drops by voltage corresponding to this quantity of charges. Therefore, the potential of the capacitor Cpd is automatically maintained at the level of (Vcc-Vth) by repeating this operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a circuit for digitizing a strobe light reception amount and a circuit for controlling a strobe light emission amount.

[0002]

2. Description of the Related Art The prior art is disclosed in Japanese Patent Application Laid-Open No. Hei 6-3085.
The invention described in No. 85 is known. FIG.
FIG. 1 is a circuit diagram showing a first example of the prior art described in the above publication. In FIG. 18, the photodiode P
D1 outputs a photocurrent proportional to the emission intensity of a strobe (not shown). The photocurrent output from the photodiode PD1 charges the capacitor C1 and charges the capacitor C1.
Is gradually increased. The potential of the capacitor C1 is
It is input to the negative terminal of the comparator CP1. Also,
The resistors R3 and R4 divide the circuit power supply voltage Vcc to form a threshold, and the threshold is input to the + terminal of the comparator CP1.

The comparator CP1 outputs Hi when the potential of the capacitor C1 is lower than the threshold, and outputs Lo when the potential is higher than the threshold. The output of the comparator CP1 is latched (sampled) by the D-type flip-flop FF1 at the cycle of the oscillation output of the oscillator OSC. Therefore, when the potential of the capacitor C1 is higher than the threshold, the D-type flip-flop F
F1 sets the output Q to Lo and the inverted output of Q to Hi. As a result, the inverted output Hi of the D-type flip-flop FF1
Is input to the switching element (analog switch) K1, and the switching element K1 is turned on.

When the switching element K1 turns on, the electric charge of the capacitor C1 is discharged via the resistor R2. As a result, the potential of the capacitor C1 decreases. However, below the threshold value, the inverted output of Q of the comparator CP1 becomes Lo. As a result, the switching element K1 is turned off, and the discharging of the capacitor C1 is stopped. As is clear from the above description, the circuit diagram shown in FIG. 18 constitutes a feedback system, and is controlled so that the potential of the capacitor C1 becomes a value near the threshold. Therefore, since the potential of the capacitor C1 is controlled to a substantially constant value, the discharge current of the capacitor C1 also becomes substantially constant. For this reason, the product of the discharge current value and the discharge period is the photodiode PD
At 1, the charge amount becomes approximately equal to the charge amount generated per unit time.

The OR circuit OR1 takes the logical sum of the Q output of the D-type flip-flop FF1 and the oscillation output of the oscillator OSC. When the output of the comparator CP1 latched by the D-type flip-flop FF1 is Lo, the OR circuit OR1 outputs a negative pulse as the output OUT only during a half cycle of the oscillation cycle of the oscillator OSC.

When the Q output of the D-type flip-flop FF1 is L
The period during which the inverted output of o and Q is Hi and the number of times a negative pulse is output to the output OUT of the OR circuit OR1 are proportional. Therefore, the number of pulses is
1 is approximately proportional to the amount of generated charge. FIG. 19 is a circuit diagram showing a second example of the prior art described in the above-mentioned Japanese Patent Application Laid-Open No. 6-308585. FIG. 19 is an improvement of the circuit shown in FIG. 18 as follows.

That is, in FIG. 18, for example, Lo (when the potential of the capacitor C1 is lower than the threshold value) is continuously output twice from the comparator CP1 to the flip-flop FF1.
, And when the sample is discontinuous like Lo-Hi-Lo, the comparator CP
Lo is output twice from 1. Therefore, in the above two cases, the discharged charge amount of the capacitor C1 must be originally the same. However, in the circuit shown in FIG. 18, the switching element (analog switch) K1 is not actually the same due to the influence of the transient characteristics at the time of ON / OFF. That is, when the output of Lo is continuous twice, the ON / OFF transient phenomenon of the switching element occurs only once. However, in the case of discontinuous occurrence such as Lo-Hi-Lo, the transient phenomenon of ON / OFF of the switching element occurs twice. As a result, due to the difference in the number of occurrences of the transient phenomenon, the amount of discharged charge of the capacitor C1 differs between the case where the sampling is performed continuously and the case where the sampling is performed discontinuously.

In the circuit shown in FIG. 19, in order to reduce the above problem, in addition to the flip-flop FF1 for latching the output of the comparator CP1, the flip-flop FF1
Flip-flop FF that latches the output of a half cycle later
2 are provided. The flip-flops FF1 and FF2 are
The switching elements (resistors R2 and R6 include the switching elements) controlled by them are turned on only during different half periods.

As a result, in the case of FIG. 18, even when the switching element K1 is continuously turned on, FIG.
In the case of 9, flip-flops FF1 and FF2 are turned on alternately. As a result, the discharge from the capacitor C1 is
The operation is performed by alternately turning on the two resistors R2 and R6 including the switching element. According to the circuit shown in FIG. 19, when the capacitor C1 discharges continuously and discontinuously, the influence of the transient characteristics becomes the same, and a constant charge can be discharged. As a result, the accuracy of measuring the amount of strobe light emission is improved.

Japanese Patent Application Laid-Open No. Sho 55-55 discloses a conventional technique for forming a digital signal indicating the amount of received light based on strobe light received by an optical sensor and controlling the emission of strobe light.
There are inventions described in JP-A-93133 and JP-B-59-33842.

[0011]

In the prior art, since the discharge through the resistor (R2, R6) is controlled by the switching element (K1 or R2, R6), the following problem arises. is there.

First, in the discharge from the capacitor (C1) storing the photocurrent of the photodiode (PD1), the discharge time is not exactly proportional to the discharge charge amount due to the influence of the transient characteristics of the switching element of the discharge circuit. . Therefore, there is a problem that the measurement accuracy of the amount of strobe light is reduced. Further, in the improved circuit shown in FIG. 19, the switching (R2, R6) of the two discharge circuits may partially overlap at the time of discharge, which affects the discharge charge amount. Therefore, the circuit shown in FIG. 19 cannot completely eliminate the influence of the transient characteristics of the switching element. Therefore, there is a problem in that the measurement accuracy of the flash emission amount becomes inaccurate because the discharge time and the discharge charge amount are not exactly proportional.

Second, in the course of discharging from the capacitor (C1), the charge potential of the capacitor (C1) changes in principle. Therefore, the assumption of constant current discharge is only approximately established. In particular, photodiodes (PD
When the photocurrent output from 1) is large, the potential fluctuation of the capacitor (C1) is large, and the measurement accuracy of the amount of strobe light emission is reduced.

Third, the threshold value of the comparator (CP1) changes according to the change of the circuit power supply voltage (Vcc). Therefore, the discharge current from the capacitor Pcd varies. Further, when the circuit power supply voltage (Vcc) changes, the reverse bias voltage of the photodiode (PD1) changes, which affects its photoelectric conversion characteristics and changes the leak current. As a result, there is a problem that the measurement accuracy of the amount of strobe light is reduced.

Fourth, the above-mentioned prior art discloses a technique for converting the amount of strobe light emission into a digital value in real time as the number of pulses. However, there is no disclosure regarding the control of the light emission amount of the strobe (light control). Therefore, there is a problem that various adjustments conventionally performed by the analog circuit are not performed by the digital circuit. For example, there is a problem that dimming control for stopping flash emission during emission is not realized by a digital circuit.

The present invention has been made in view of the above-mentioned problems of the prior art, and has the following objects. A first object is that when a certain amount of storage is discharged from a storage unit that stores the output of a photoelectric conversion unit such as a photodiode, the measurement accuracy of the strobe light emission amount is not reduced due to the influence of switching in the certain amount discharge unit. An object of the present invention is to provide a circuit for digitizing an amount of received strobe light.

A second object of the present invention is to store a strobe light emission amount as electric charge and discharge the accumulated electric charge, thereby strobe light receiving amount digitizing circuit which does not reduce measurement accuracy of the strobe light emission amount due to switching effect of a discharge circuit. An object of the present invention is to provide a strobe light emission amount control circuit.

A third object of the present invention is to provide a circuit for digitizing the amount of received strobe light and a circuit for controlling the amount of emitted strobe light, which do not degrade the accuracy of measuring the amount of emitted strobe light with respect to fluctuations in the circuit power supply voltage. A fourth object is to provide a strobe light receiving amount digitizing circuit and a strobe light emitting amount control circuit realized by a digital circuit so as to obtain a high accuracy with respect to dimming control for stopping strobe light emission during light emission. .

[0019]

According to a first aspect of the present invention, there is provided a strobe light receiving amount digitizing circuit, comprising: photoelectric conversion means for receiving light from a strobe and generating an output corresponding to the intensity of the received light; A storage means for storing the generated output, and, when the storage amount of the storage means exceeds a predetermined threshold, the storage means synchronizes with a predetermined sampling frequency and performs a predetermined storage from the storage means for a predetermined period shorter than the sampling cycle. Release the amount, feedback control the accumulation amount of the accumulation means, a constant amount release means to keep the accumulation amount of the accumulation means near a constant value, and when the accumulation amount of the accumulation means exceeds a predetermined threshold, And a light receiving amount output means for outputting a pulse signal.

According to a first aspect of the present invention, in the circuit for digitizing the amount of received strobe light, the constant amount emitting means always synchronizes with a predetermined sampling frequency and emits a fixed amount of storage during a predetermined period shorter than a sampling period. Therefore, the release time and the release accumulation amount are exactly proportional. Therefore, the measurement accuracy of the strobe light emission amount, that is, the photocurrent can be greatly improved.

According to a second aspect of the present invention, a strobe light receiving amount digitizing circuit receives light from a strobe and outputs a current corresponding to the intensity of the received light, and accumulates a current output from the photoelectric conversion means. To convert to a voltage value
When the voltage value output from the voltage conversion means and the current / voltage conversion means exceeds a predetermined threshold, the current / voltage is synchronized with a predetermined sampling frequency and in a predetermined period shorter than a sampling period. Constant current discharging means for discharging a constant current from the converting means, feedback-controlling the output voltage of the current / voltage converting means, and maintaining the voltage output from the current / voltage converting means near a constant voltage; and A light-receiving amount output unit that outputs a pulse signal when a voltage value output from the unit exceeds a predetermined threshold.

According to a second aspect of the present invention, in the strobe light receiving amount digitizing circuit, the constant current emission means always discharges a constant current during a predetermined period shorter than the sampling period, in synchronization with a predetermined sampling frequency. The discharge time and the discharge amount are exactly proportional. Therefore, the amount of flash emission,
That is, the measurement accuracy of the photocurrent can be greatly improved. Also, the number of pulses output from the received light amount output means can accurately indicate the amount of strobe light received.

According to a third aspect of the present invention, there is provided a circuit for digitizing the amount of received strobe light, wherein the constant current discharge from the current / voltage converting means is performed over a half cycle of the sampling cycle. It is characterized by being performed. According to the third aspect of the present invention, the constant current discharge from the current / voltage converter is performed over a half cycle of the sampling cycle.
There is no continuous discharge from the current / voltage conversion means. Therefore, since one discharge is always performed by one transient phenomenon, an error of constant current discharge due to overlapping of transient phenomena can be reliably removed.

According to a fourth aspect of the present invention, there is provided a digitizing circuit for receiving a strobe light according to the second aspect, wherein the constant current changes in accordance with the aperture value of the camera and the film sensitivity. . In the circuit for digitizing the amount of light received by a strobe according to claim 4, the constant current varies according to the aperture value of the camera and the film sensitivity.
The measurement accuracy of the flash emission amount can be adjusted to an appropriate value according to the aperture value and the film sensitivity.

According to a fifth aspect of the present invention, there is provided a strobe light receiving amount digitizing circuit according to the fourth aspect, wherein the constant current which changes according to the aperture value of the camera and the film sensitivity is a plurality of predetermined values. The current value is selected from the following. The strobe light receiving amount digitizing circuit according to the fifth aspect can easily adjust the constant current according to the aperture value of the camera and the film sensitivity.

According to a sixth aspect of the present invention, there is provided a digital circuit for strobe light reception amount according to the fifth aspect, wherein a plurality of current values specific to the manufactured circuit are used as the plurality of current values. And The electronic circuit for digitizing the amount of light received by a strobe according to claim 6 uses a plurality of current values specific to the manufactured circuit as the plurality of current values, so that it is not necessary to take special measures on the circuit.

According to a seventh aspect of the present invention, there is provided a digital circuit for strobe light receiving amount according to the second aspect of the present invention, wherein the means for stabilizing a reverse bias voltage of the photoelectric conversion means and the threshold value are a circuit power supply voltage. And means which are not affected by the above. Claim 7
The described strobe light receiving amount digitizing circuit can effectively prevent a decrease in the measurement accuracy of the strobe light emission amount (photocurrent) and a decrease in the strobe light control accuracy due to the fluctuation of the circuit power supply voltage.

In accordance with another aspect of the present invention, a strobe light emission amount control circuit receives light from the strobe and outputs a current corresponding to the intensity of the received light, and accumulates a current output from the photoelectric conversion means. Current-voltage conversion means for converting the voltage to a voltage value, and when the voltage value output from the current-voltage conversion means exceeds a predetermined threshold value, the predetermined value is synchronized with a predetermined sampling frequency and shorter than the sampling period. During the period, the constant current is discharged from the current / voltage conversion means, the output voltage of the current / voltage conversion means is feedback-controlled, and the voltage output from the current / voltage conversion means is held near a constant value. Means, a received light amount output means for outputting a pulse signal when a voltage value output from the current / voltage conversion means exceeds a predetermined threshold, and a pulse signal Collected by, when the count value exceeds the comparison value predetermined, characterized in that it is composed of a flash light emission stop means for outputting a light emission stop signal to the flash.

The strobe light emission amount control circuit according to the eighth aspect of the present invention is characterized in that the constant current discharging means always discharges a constant current during a predetermined period shorter than a sampling period in synchronization with a predetermined sampling frequency. Time and discharge amount are exactly proportional. Therefore, the measurement accuracy of the strobe light emission amount, that is, the photocurrent can be greatly improved. Also, the number of pulses output from the received light amount output means can accurately indicate the amount of strobe light received. further,
Strobe light emission stop means counts the number of pulses, and outputs a light emission stop signal to the strobe when the count value exceeds a predetermined comparison value. High accuracy can be obtained.

According to a ninth aspect of the present invention, in the strobe light emission amount control circuit according to the eighth aspect,
The comparison value is set to a value smaller than a design comparison value determined by the aperture value and the shooting distance. The strobe light emission amount control circuit according to the ninth aspect can reduce the influence of an error called brightening in which light emission continues after the light emission stop signal is output.

According to a tenth aspect of the present invention, in the strobe emission amount control circuit according to the ninth aspect,
The comparison value is characterized in that it gradually changes over time after the start of flash emission. Claim 1
In the strobe light emission amount control circuit described in No. 0, since the comparison value changes stepwise with the elapse of time after the start of the strobe light emission, it is possible to adjust the timing of outputting the light emission stop signal. Therefore, it is possible to reduce the influence of the error called the brightening.

According to a eleventh aspect of the present invention, in the strobe emission amount control circuit according to the eighth aspect,
The strobe light emission stopping means counts the number of pulse signals based on the very small amount of light emitted by the strobe, and, based on the count result, generates a constant current at the time of main light emission following the very small amount of light from a plurality of predetermined current values. It is characterized by selecting.

According to the eleventh aspect, the strobe light emission amount control circuit determines a constant current at the time of main light emission based on a count value of a pulse signal based on light emission of a small amount of light before main light emission. Can be reduced. A strobe light emission amount control circuit according to a twelfth aspect of the present invention is the strobe light emission amount control circuit according to the eleventh aspect, wherein the plurality of predetermined current values are exponential series of powers of two.

In the strobe light emission amount control circuit according to the twelfth aspect, since the plurality of current values are an exponential series of powers of two, the implementation of an IC is facilitated and the dynamic range can be covered. According to a thirteenth aspect of the present invention, in the strobe light emission amount control circuit according to the eleventh or twelfth aspect, a plurality of predetermined constant current values and a plurality of constant current values realized by an actual circuit are provided. And a correction means for correcting a predetermined comparison value based on the difference between the constant current values stored in the memory.

The flash light emission amount control circuit according to the thirteenth aspect corrects the comparison value based on a difference between a predetermined constant current value and a constant current value realized by an actual circuit. Dimming control can be performed accurately.

[0036]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. This embodiment corresponds to the first to third aspects of the present invention. In the strobe light receiving amount digitizing circuit shown in FIG. 1, Vcc is a circuit power supply voltage, PD
Is a photodiode for detecting strobe light, Rpd is a resistor for preventing latching of the photodiode PD, Cpd is a capacitor for converting charges generated by the photodiode PD into a voltage, C
MP is a comparator, BA is a power supply for outputting a bias voltage Vth applied to the negative terminal of the comparator CMP, FF is a D-type flip-flop, NAND is a NAND circuit, CS1
Indicates a constant current source.

Here, the comparator CMP outputs Hi when the potential of the capacitor Cpd is higher than (Vcc-Vth), and outputs Lo when it is lower. The D-type flip-flop FF is
Comparator CM at rising edge of sample clock CK
The output of P is sampled. In addition, NAND circuit NAN
D is the NAND of the output of the D-type flip-flop FF and the inverted input of the sample clock CK.

Specifically, a D-type flip-flop FF
Latches the output of the comparator CMP at the rising edge of the sample clock CK every time. Assuming that the output of the comparator CMP is Hi, the D-type flip-flop FF
Latches Hi at the rising edge of the sample clock CK and outputs Hi as the Q output. Next, during the period of Lo when the sample clock CK falls, only when the Q output of the D-type flip-flop FF is Hi, the NAND circuit NA
ND outputs Lo.

That is, when the sample clock CK is a half cycle of Lo, the comparator CMP sampled immediately before
Is high, the output of the NAND circuit NAND is Lo.
become. If the above condition is not satisfied, the NAND circuit NAN
D always holds the output Hi. When the output of the NAND circuit NAND is Lo, the constant current source CS1 becomes active.
When the constant current source CS1 becomes active, the capacitor Cpd
, A constant charge is discharged.

In the above configuration, the correspondence with the components described in the claims is as follows. That is, the photodiode PD corresponds to the photoelectric conversion unit. The storage means and the current / voltage conversion means are a capacitor C
pd, the constant amount discharge means and the constant current discharge means are a comparator CMP, a D-type flip-flop FF, and a NAND circuit NAN.
D corresponds to the constant current source CS1. The received light output means is D
The type flip-flop FF corresponds to the NAND circuit NAND.

Next, the circuit operation of the first embodiment shown in FIG. 1 will be specifically described. In the circuit shown in FIG. 1, the photocurrent generated from the photodiode PD charges the capacitor Cpd. As a result of charging, when the potential of the capacitor Cpd exceeds (Vcc-Vth), the comparator CMP
Becomes Hi. Output Hi of comparator CMP
Is latched by the D-type flip-flop FF at the rise of the sample clock CK, and the constant current source CS1 becomes active in the next half cycle of Lo of the sample clock CK. Therefore, the capacitor Cpd discharges a constant charge during this period, and the potential of the capacitor Cpd decreases by an amount corresponding to this charge. Therefore, by repeating the above operation, the potential of the capacitor Cpd automatically becomes (Vcc-V
th) level. That is, the first type shown in FIG.
The circuit according to the embodiment constitutes a feed hack circuit in the same manner as in the prior art shown in FIG.

FIG. 2 is a time chart showing an operation example of the first embodiment shown in FIG. 1, and shows a circuit operation when a constant photocurrent is output from the photodiode PD. FIG. 2 shows the bias voltage Vth, the potential of the capacitor Cpd, the output of the comparator CMP, and the sample clock CK.
And the output of the NAND circuit NAND. As shown in FIG. 2, the output of the comparator CMP is detected at the rise of the sample clock CK. Next sample clock CK
At the fall, the detection result appears at the output of the NAND circuit NAND. Therefore, there is a delay of 1/2 cycle of the minimum sample clock CK and 1 cycle of the maximum sample clock until the output inversion of the comparator CMP is fed back to ON / OFF of the constant current.

In the circuit shown in FIG. 1, a NAND circuit NAND
The discharge of the charge stored in the capacitor Cpd is performed only during the period when the sample clock CK is Lo. That is, the period during which the constant current discharge is performed is only a half cycle of the sample clock CK, and is not continuously turned on. In addition, since the circuit operation of one constant current discharge is always the same, even for the distortion of the electric discharge waveform,
The proportional relationship between the number of times of discharge and the amount of discharge charge can be maintained. This corresponds to the third aspect of the present invention.

Therefore, FIG.
As described above, there is no need to provide a complicated circuit (FF1, FF2, etc.) that divides the discharge into separate half cycles. Also,
The amount of discharge per pulse output from the NAND circuit NAND can be adjusted by adjusting the constant current source CS1. Alternatively, the discharge amount per pulse may be measured in advance, stored in a non-volatile memory (not shown), read out, and used as a constant current discharge value.

The first embodiment shown in FIG. 1 is designed to prevent the circuit operation from becoming unstable even if the circuit power supply voltage Vcc fluctuates. Specifically, the voltage applied to the photodiode PD is stabilized at Vth, and the capacitor C
This is because a constant current that does not depend on the circuit power supply voltage Vcc is used for discharging pd. Therefore, according to the circuit of FIG.
Even if the circuit power supply voltage Vcc is different, the photodiode PD
Output the same photocurrent, the same number of pulses are output from the NAND circuit NAND. Of course, in an actual electric element, the constant current property of the constant current circuit slightly depends on Vcc. However, as compared with the examples of FIG. 18 and FIG. 19 described in the section of the prior art, the stability is much higher.

The actual light emission of the strobe is several hundreds.
It is a short flash of μs. In order for the circuit shown in FIG. 1 to convert the flash into a pulse in real time, the frequency of the sample clock CK must be increased and the responsiveness of the circuit must match the frequency. In the flash light control, the number of pulses is counted and compared with a threshold value, and a light emission stop signal is output. Therefore, the sample clock CK
Will determine the accuracy of the generation timing of the light emission stop signal. Practically, it is appropriate that the frequency of the sample clock CK is approximately 4 MHz to 8 MHz. 4
In the case of MHz, the resolution is 250 ns, and in the case of 8 MHz, the resolution is 125 ns.

It is theoretically possible to increase the accuracy by further increasing the frequency. However, it is difficult to switch the constant current at a very high speed and stabilize the integrated charge amount in terms of a circuit. Also, the input of the comparator CMP is an MO that can ignore the bias current.
An S transistor input is desirable. However, the input of the comparator CMP is usually a bipolar transistor input when the high-speed response is required. For example, when the input stage of the comparator CMP is a PNP transistor input, the bias current of the human input terminal is added to the photodiode current, resulting in a measurement error. Normally, the input bias current is equivalent to the photocurrent and charges the capacitor Cpd. Therefore, the comparator CMP sometimes inverts to Hi, and the NAND circuit NAND outputs a pulse. Therefore, even if the photocurrent is zero in the dark state, an error occurs due to the input bias current. Generally, in circuit design, a comparator CMP is designed so as to reduce a bias current while ensuring responsiveness, or a comparator C with a smaller bias current is used from a commercially available one.
MP will be selected. The method of correcting the error will be described later in detail.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention. This embodiment corresponds to the first to third aspects of the present invention. FIG. 3 is a more concrete example of the circuit shown in FIG. 1 in consideration of the circuitization of the circuit shown in FIG. The operation of the constant current source CS1 shown in FIG. 3 will be described. 3, the same parts as those in FIG. 1 are denoted by the same reference numerals. In FIG. 3, R1, R2, RL are resistors, REG is a constant voltage circuit, RT is a variable resistor, Tr1, T
r2, Tr3, Tr4, Tr5 are transistors, D2 is a diode connected in series, D3 is a diode connected in series, and D4 is a diode connected in series.

The constant voltage circuit REG and the transistor Tr
1, Tr2, Tr3, Tr4, Tr5, Diode D
2, D3, D4 and the like constitute the constant current source CS1 shown in FIG. More specifically, the constant voltage circuit RE
G and the transistors Tr3, Tr4, Tr5 form a constant current circuit, and the constant current flows between the collector and the emitter of the transistor Tr3. In the following description, VF means a potential drop of one diode. The output of the NAND circuit NAND is open drain.

In the above configuration, the correspondence with the configuration requirements described in the claims is as follows. That is, the photodiode PD corresponds to the photoelectric conversion unit. The storage means and the current / voltage conversion means are capacitors Cp
d, the constant amount discharge means and the constant current discharge means are composed of a comparator CMP, a D-type flip-flop FF, and a NAND circuit NAN.
D corresponds to the constant current source CS1 composed of the above elements. The received light amount output means is a D-type flip-flop FF
And a NAND circuit NAND.

When the output of the NAND circuit NAND is Hi,
The base potential of the transistor Tr1 becomes four times the potential drop VF due to the presence of the diode D4. On the other hand, the base potential of the transistor Tr2 is the diode D
The presence of 3 makes the potential drop VF three times. Therefore, all the constant current output flowing between the collector and the emitter of the transistor Tr3 flows through the transistor Tr1. Therefore, when the output of the NAND circuit NAND is Hi, discharge from the capacitor Cpd does not occur.

On the other hand, when the photocurrent is charged in the capacitor Cpd and the output of the comparator CMP becomes Hi,
As described above, the NAND circuit NAND outputs Lo for a half cycle of the sample clock CK being Lo. Therefore, the base potential of the transistor Tr1 is
2, the potential drops to almost twice the potential drop VF. As a result, the constant current output flowing between the collector and the emitter of the transistor Tr3 does not flow through the transistor Tr1, but flows through the transistor Tr2.
The current flowing through the transistor Tr2 extracts the charge stored in the capacitor Cpd. Thus, when the output of the comparator CMP becomes Lo again, the NAND circuit NAN
D outputs Hi, the transistor Tr1 is turned on, the transistor Tr2 is turned off, and the constant current extraction from the capacitor Cpd stops.

The circuit shown in FIG. 3 has the following advantages as compared with the case where the transistor is simply turned on / off to extract a constant current from the constant voltage circuit. That is, in the configuration in which the transistor is simply turned on / off to extract a constant current from the constant voltage circuit, response delay and transient distortion are extremely large. In contrast, FIG.
The circuit shown in FIG. 1 incorporates the principle of a differential circuit into the constant current source CS1 shown in FIG. 1 to realize a high-speed response. FIG.
The circuit shown in (1) shows relatively good characteristics with respect to transient distortion.

In the circuit shown in FIG. 3, the bias voltage Vth shown in FIG. 1 is provided by a diode Dc, a resistor Rc, and a capacitor Cc. Since the reverse bias potential of the diode Dc is stable, the bias voltage V
th is stabilized independently of the circuit power supply voltage Vcc. As described above, a constant current independent of the circuit power supply voltage Vcc is used for discharging the capacitor Cpd. As a result, in the circuit shown in FIG. 3, as in the circuit shown in FIG. 1, care is taken not to make the circuit operation unstable even if the circuit power supply voltage Vcc fluctuates. This corresponds to the invention described in claim 7.

Next, adjustment of the constant current value, measurement accuracy, and switching of the constant current will be described. The circuit shown in FIG.
It can be provided on the strobe side or on the camera side. In the following description, it is assumed that the circuit shown in FIG. 3 is provided on the strobe side. in this case,
The photometric photodiode PD always receives the subject reflected light at the same aperture.

FIG. 4 shows the photodiode PD shown in FIG.
FIG. 5 is a diagram showing a (full) emission waveform of a general strobe light received by the strobe. The horizontal axis indicates time, and the vertical axis indicates photocurrent. The effect of the lens aperture does not occur because the circuit is provided on the strobe side. Therefore, the waveform of the photocurrent shown in FIG. 4 has a similar shape regardless of the distance. However, since the reflected light becomes stronger as the subject distance is shorter, the reflected light decreases as the subject gets farther. The photocurrent increases or decreases in principle in inverse proportion to the square of the subject distance.

When strobe light having a waveform as shown in FIG. 4 is measured using the circuit shown in FIG. 3, the potential of the capacitor Cpd is maintained at Vth even when the photocurrent of the photodiode PD has a peak value. Thus, it is necessary to determine a constant current value for extraction. In the circuit shown in FIG. 3, since the constant current is discharged only for a half cycle of the sample clock CK, the constant current value needs to be set to a value twice or more the peak value of the photocurrent. Therefore, it is necessary to set a constant current value at least twice the peak value of the photocurrent at the closest control distance.

In FIG. 4, the area of the emission waveform (total amount of received light) is S, the peak current is Lpeak, and the sample period is △.
T (ΔT = 1 / CK), and the constant current in FIG.
If it is set to Lpeak, the total number of pulses N is as follows: N = S / (Lpeak △ T) (1)

From equation (1), it can be seen that in order to convert the same total received light amount S into a larger number of pulses N, Lpeak · ΔT may be reduced. ΔT decreases as the sampling frequency increases, and Lpeak decreases as the peak current decreases. FIG. 5 is a diagram showing an emission waveform when the distance is the same, the total amount of received light S is the same, and the peak current is reduced, as compared with the example shown in FIG. As shown in FIG. 5, the light emission waveform becomes a flat waveform.

The flattening of the light emission waveform is not limited to the circuit for digitizing the amount of received strobe light described in the present embodiment, but is an improvement that makes it easy to control the conventional analog system. However, flattening the light emission waveform in order to convert the same total received light amount S into a larger number of pulses N increases the inductance inserted in series in the light emitting circuit. Therefore, in practice, some compromise must be made from the size of the inductor and its current capacity.

The constant current value must be set to at least twice the peak value Lpeak of the photocurrent, assuming that the extraction of the constant current is performed only for a half cycle of the sampling cycle. As a result, it is possible to prevent the delay of the circuit due to causes other than the sampling, and it is possible to maximize the detection capability. As described above, FIGS. 1 and 3
, The constant current value is the peak value Lpeak of the photocurrent.
Must be at least twice as large. However, as the constant current value is increased, the negative pulses output from the NAND circuit NAND become increasingly sparse.
This is because, in the circuits shown in FIG. 1 and FIG. 3, the resolution of the flash detection of strobe light decreases, and the detection delay increases. Therefore, the constant current value cannot be made too large. Practically, it is determined as follows in consideration of an appropriate operation of the circuit and a margin for circuit adjustment. That is, the constant current value is obtained by measuring the photocurrent peak value Lpeak when the strobe light is emitted at the closest shooting distance (usually 0.5 m to 0.75 m) and adjusting the constant to approximately three times the photocurrent peak value Lpeak. Is appropriate.

Next, the external light control of the strobe, that is, the light emission amount control by the strobe itself will be described. When the strobe side controls the light emission amount, the light reflected from the subject is received by the photodiode of the strobe main body, and a pulse corresponding to the received light amount is generated. When the number of pulses reaches a predetermined value, a light emission stop signal is output. With this light emission stop signal, the light emitting tube (xenon tube) of the strobe is turned off.
This is called "automatic light control mode". Here, "external" means an external (strobe-side) dimming circuit that does not depend on the dimming circuit in the camera.

FIG. 6 is a circuit diagram showing a third embodiment of the present invention. The embodiment shown in FIG. 6 shows a flash light emission amount control circuit for generating a light emission stop signal by using the flash light reception amount digitizing circuit shown in FIG. This embodiment corresponds to the eighth aspect of the present invention.

FIG. 6 shows the counter 10 counting the output pulses from the flash light emission amount control circuit shown in FIG. If the count value matches the comparison value, the one-shot timer 12 at the subsequent stage outputs a light emission stop signal. It is assumed that the counter 10 shown in FIG. 6 is cleared in response to a light emission start signal output from the camera. The light emission stop signal is a few μs
It is a short signal of c. After the clearing is canceled in response to the light emission start signal, the counter 10 counts up the light amount of the strobe light emission from zero. There are many disclosed examples and products of the circuit technology for stopping the strobe light emission, which are well-known and will not be described here.

The correspondence between the third embodiment and the constituent features of the invention described in claim 8 is basically the same as that of the first embodiment shown in FIG. However, the flash emission stopping means of claim 8 corresponds to the counter 10, the digital comparator 11, and the one-shot timer 12. In the following description, the closest shooting distance is 0.5 m, the constant current value is twice the current value of the peak value of the photocurrent, the maximum pulse count value in the counter 11 at the time of full light emission (hereinafter, full light emission pulse). 10)
000 pulses. Each value is a sample clock C
If K is 4 to 8 MHz, it is a realistic numerical value.

FIGS. 7 and 8 show examples of the number of stop pulses and the number of full emission pulses at each aperture value and each distance under the above conditions. The number of stop pulses and the number of full emission pulses are shown in fractional format. The denominator is the number of full emission pulses, and the numerator is the number of stop pulses. The number of full light emission pulses is the same if the distance is constant,
Increases or decreases in inverse proportion to the power.

As is apparent from FIG. 7, the number of full light emission pulses is 10,000 at a distance of 0.5 m. However, as is clear from FIG.
At a distance of 5.6 m, it decreases to 78 pulses. Also, in a camera, the appropriate exposure amount is, if the aperture value is the same,
It is constant regardless of the distance. Therefore, the number of stop pulses at each aperture value is also constant. Changing the ISO value (film sensitivity) is the same as changing the aperture value from the viewpoint of light quantity control. Therefore, in FIGS. 7 and 8, each ISO value and aperture value are shown on the left.

As is apparent from FIGS. 7 and 8, the ISO
When the value and the aperture value are known, the number of stop pulses is determined. That is, the number of stop pulses is not affected by the shooting distance. The number of stop pulses is set as a comparison value input to the digital comparator 11 shown in FIG. The ratio of the number of stop pulses to the number of full light emission pulses indicates the output timing of a light emission stop signal during strobe light emission. For example, as is clear from FIGS. 7 and 8, the ratio of the number of stop pulses to the number of full light emission pulses is "a distance of 0.5 m in ISO 100 and 2500/10000 at an aperture value of f32", and "IS
At O100, the distance is 1 m, and at the aperture value f16, 625.
/ 2500 ”and“ distance 2 in ISO100 ”
m, aperture value f8, 156/625 ”and“ IS
At O100, a distance of 4 m and an aperture value of f4 are 39/1.
56 ". That is, the ratio of the number of stop pulses to the number of full emission pulses in each case is 1 /
It becomes 4. Therefore, in each case, the timing of outputting the light emission stop signal is the same.

However, it is difficult for the strobe light emission amount control circuit to accurately control the strobe light control when the number of stop pulses is small. This is because the light receiving amount of the light receiving sensor (photodiode PD) of the strobe light emitting amount control circuit is attenuated as the subject is located farther away (inversely proportional to the square of the distance). This is because, in the circuit shown in FIG. 6, the number of occurrences of the output pulse is reduced due to the fixed current value being a fixed value.

FIGS. 9A and 9B are diagrams showing the amount of light received by the photodiode PD when the same amount of strobe light is applied to a subject at a short distance and a subject at a long distance. FIG. 9A shows the case of a short-distance subject, and FIG. 9B shows the case of a long-distance subject. FIG.
In addition, in the circuits shown in FIGS. 3 and 6, as the distance becomes longer, the generation of the output pulse becomes sparser, and the time measurement accuracy deteriorates. In the automatic light control mode, when the aperture value is bright and the ISO value is high at a long distance, control accuracy becomes a problem particularly. For example, as is apparent from FIG. 8, in the ISO 400, at the aperture value f2 and the distance of 4 m, the ratio of the number of stop pulses to the number of full light emission pulses is 2/156. Similarly, as is clear from FIG. 8, in the ISO 400, the aperture value f2 and the distance 5.6.
At m, the ratio of the number of stop pulses to the number of full light emission pulses is a very rough value of 2/78.

By knowing in advance the number of full light emission pulses corresponding to the shooting distance, the constant current value in FIGS. 1, 3 and 6 can be set smaller in proportion to this. Thus, in the circuits shown in FIGS. 1, 3 and 6, the number of full light emission pulses can be the same regardless of the shooting distance. If this method can be realized, the problem of the control accuracy will be solved.

However, the constant current value is such that the photographing distance is 0.
In the case of 10 steps from 5 m to 16 m, it is necessary to set at a ratio of 1024 times. It is actually difficult to operate the circuits shown in FIGS. 1, 3 and 6 in the above-described large current range. In order to know the shooting distance, it is necessary to have the camera transmit lens distance information. However, the distance information may have a large error. Further, even at the same shooting distance, the number of full light emission pulses greatly differs depending on the reflectance of the subject and the state of the background. Therefore, in the circuits shown in FIGS. 1, 3 and 6, it is difficult to increase the control accuracy by setting the constant current value small in proportion to the shooting distance.

As can be seen from FIGS. 7 and 8, the shooting distance at which the number of stop pulses is equal to the number of full light emission pulses differs depending on each aperture value. In FIGS. 7 and 8, the number of stop pulses is equal to the number of full light emission pulses in the lowest column at each distance. For example,
If the distance is 0.5m, it is 10,000 / 10,000, and the distance is 0.
If it is 7m, it is 5000/5000. If the aperture value is small, the amount of light on the film surface increases, so that it is naturally possible to shoot at a long distance. Conversely, if the aperture value is increased by one step, the reach distance of the strobe light becomes 0.707 times, and it becomes difficult to shoot up to a long distance.

In FIGS. 7 and 8, the photographing limit at a short distance differs depending on each aperture value. For example, the imaging limit at a distance of 0.5 m is a combination of each ISO value and aperture value in which the ratio of the number of stop pulses to the number of full emission pulses satisfies the condition of 39/100000. For example, IS
There are a combination of O100 and an aperture value of 4, a combination of ISO200 and an aperture value of 5.6, and the like.

It should be noted that even under the conditions of ISO 100, a distance of 0.5 m, and an aperture value of 1.4, the number of stop pulses is calculated. However, in this case, the flash emission
Extremely weak light emission is obtained, and control becomes difficult. For this reason,
7 and 8, the limits are ISO 100, a distance of 0.5 m, and an aperture value of 4. In addition, the short-distance shooting limit extends to an aperture value one step brighter when the distance is one step farther. In FIG. 7, the limit is the number of stop pulses: the number of full light emission pulses = 39: 10000, but this ratio changes according to the ability of the control circuit.

The reason why it is difficult to control the minute light emission is mainly due to the properties of the arc tube (xenon tube) and the delay time of the control circuit. That is, it takes some time from when the light emission stop signal is output from the circuit shown in FIG. 6 to when light emission actually stops. FIGS. 10A and 10B are diagrams showing the relationship between the amount of light received by the photodiode PD and time, and particularly show the state from when the light emission stop signal is output to when light emission stops.

FIG. 10A shows a case where a light emission stop signal is output at a relatively early timing after the start of flash light emission. FIG. 10B shows a case where a light emission stop signal is output at a later timing after the start of flash light emission. FIG. 10B shows a case where a light emission stop signal is output after most of the light emission of the total amount of light emission of the strobe light is completed.

In FIGS. 10A and 10B, the area S
1, S3 indicates the light emission amount at which the light emission stop signal is output from the start of the flash light emission. In addition, FIG.
In (b), the areas S2 and S4 are the light emission amounts after the light emission stop signal is output, and are control error amounts called “brightening”. If the areas S2 and S4 are zero, no control is required. However, as the fractional ratio (the number of stop pulses / the number of full emission pulses) in FIGS. 7 and 8 decreases, the areas S2 and S4 increase. As a result, when the fraction ratio becomes small, a situation occurs in which the amount of light emitted from the strobe greatly exceeds the control target. Thus, the fractional ratio is
Set it to a certain value or more, and set this value as the limit of the controllable range. The situation described above is the same in the conventional analog control system, and there is a limit to the controllable range in the automatic dimming in the analog control system as in FIGS.

A method for preventing the dimming (control) accuracy of the flash emission amount from being reduced in a range where the fractional ratio is small (for example, photographing with a small aperture value) will be described. This method changes the constant current value in FIG. 6 (the same applies to FIGS. 1 and 3) according to the aperture value. 7 and 8, the number of full light emission pulses was 10,000. This means that the frequency of the sample clock CK is determined in FIG.
In this case, the constant current value is determined as a result of determining the constant current value so that the circuit of the capacitor Cpd does not overflow even for a moment due to the photocurrent of the photodiode PD.

If it is known beforehand that the light emission stop signal is output before the photocurrent of the photodiode PD reaches the peak value, the constant current value is set to a smaller value to increase the resolution of the light emission amount detection. Lighting (control) accuracy can be increased. For example, according to ISO100 and F16, the fractional ratio in FIG. 7 is 625/10000, and it is clear that the light emission stop signal is output before the light emission reaches 10% of the full light emission amount. The fraction ratio increases as the shooting distance increases. However, since the peak current itself decreases in inverse proportion to the square of the distance, the circuit of the capacitor Cpd does not overflow due to the photocurrent.

FIGS. 11 and 12 are diagrams showing the relationship between the number of stop pulses and the number of full emission pulses at each ISO value, each aperture value, each distance, and each constant current ratio. In FIGS. 11 and 12, the peak of the photocurrent is about 25 times the full emission pulse number.
% To about 35%, and I
An example in which a constant current value is set according to an SO value and an aperture value is shown.

The “constant current ratio” shown in FIG. 11 and FIG.
When the fixed constant current shown in FIGS. 7 and 8 is “1”,
It shows the ratio with the constant current actually flowing in the circuit. 11 and 12, the constant current ratio is set to 1/8 at the aperture values f4 and f5.6 in, for example, ISO100. Therefore, the detection resolution of the photocurrent can be improved by eight times compared with the case of FIGS. 7 and 8.

According to the circuits shown in FIGS. 1, 3 and 6, as shown in FIGS. 11 and 12, the control accuracy of the output timing of the light emission stop signal is improved by changing the constant current ratio. Is possible. However, with the discharge of the photocurrent via the resistor described in the section of the prior art, such an improvement in control accuracy cannot be realized, and the advantages of the present embodiment can be understood.

In FIGS. 11 and 12, the constant current ratio based on the aperture value is selected in an exponential series of 2 (1, 1/2, 1/4...) To cover the dynamic range. This corresponds to the invention described in claim 12. However, the present invention provides
However, the present invention is not limited to the exponential series, and a plurality of constant current values may be prepared and selected. This corresponds to the fourth and fifth aspects of the present invention.

Further, the constant current flowing through the circuits shown in FIGS. 1, 3 and 6 is changed to a predetermined current value (for example, 1 /
It is easier to use each constant current actually flowing in the circuit as it is than to adjust the current ratio to (2, 1/4...). This corresponds to the invention described in claim 6. Then, the ratio to each constant current value or a certain reference current value actually flowing in the circuit is stored in a non-volatile memory, and a comparison value to be input to the digital comparator 11 shown in FIG. 6 is set according to the storage contents of the memory. Is preferred. For example, FIG.
3 and 6, when the design value of the constant current is different from the constant current actually flowing through the completed circuit, the deviation amount is stored in a nonvolatile memory (not shown), and the stored deviation is stored. The light emission amount is corrected based on the light amount. Specifically, it is realized by the CPU of the strobe (not shown) correcting the comparison value input to the digital comparator 11 of FIG. 6 by the number of pulses corresponding to the shift amount read from the memory (not shown). The above description corresponds to the invention of claim 13.

Changing the setting of the constant current value in accordance with the aperture value contributes to improving the accuracy of the output timing of the light emission stop signal. However, this does not contribute to the improvement of the control error due to the light increase described with reference to FIGS. 10 (a) and 10 (b). Since it is physically impossible to make the brightness increase to zero, the conventional analog control is devised so as to reduce the brightness increase by performing various corrections. In brief, in FIGS. 10A and 10B, the areas S2 and S4 for the light increase are predicted, and a light emission stop signal is output earlier to bring the light emission amount closer to the areas S1 and S3.

However, as can be seen from FIGS. 10A and 10B, the ratio of the area S2 to the area S1 and the ratio of the area S4 to the area S3 depend on the emission time until the emission stop signal is output. Changes greatly. As the subject approaches the strobe and the ISO value increases, it is necessary to stop light emission in a short light emission time. This is because, in such a case, the area (S2) of the increased light cannot be ignored with respect to the area (S1). However, when the light emission time becomes long as shown in FIG. 10B, the area S4 becomes negligible with respect to the area S1.

Next, several techniques for correcting the increased light (S2, S4) will be described. First, a method of setting a comparison value to be input to the digital comparator 11 in FIG. 6 by subtracting an appropriate fixed value from a certain threshold will be described. This corresponds to the ninth aspect of the present invention.

From the nature of the brightening described above, subtracting an appropriate fixed value from the threshold value to obtain a comparison value is in principle incomplete. However, this method is effective in averaging dimming errors at short distances and long distances. For example, as is clear from FIGS. 7 and 8, ISO100, F5.
6. At a distance of 0.5 m, 78 pulses are the number of stop pulses. Here, it is assumed that at a distance of 0.5 m, S2 / S1 is 0.5 (corresponding to 0.5 EV), and that an error at a long distance is zero. In this case, if the normal control is performed, the distance becomes 0.5 EV when the distance is 0.5 m. However, by setting a comparative value by subtracting an appropriate fixed value from the threshold value, for example, it is possible to assign the value -0.25 EV under at a long distance and 0.25 EV over at 0.5 m. This method is simple and quite effective in practice.

When a method of setting a comparison value to be input to the digital comparator 11 in FIG. 6 by subtracting an appropriate fixed value from the certain threshold value is used, as shown in FIG. 7 and FIG. Then, the rule that the comparison value is doubled is broken. Practically, a value that enables dimming control from a short distance to a long distance to be executed in a balanced manner is searched for and stored in a nonvolatile memory as an adjustment element. Further, since the subtraction value from the comparison value when the aperture value or the ISO value changes is different, each value is stored.

Second, a method for correcting the comparison value with time will be described. The rate at which the brightening contributes to the control error (the ratio of S2 to S1 shown in FIG. 10A) is
It is affected by the output timing of the light emission stop signal. Therefore, after the strobe light emission is started, the comparison value is dynamically changed with time. This corresponds to the tenth aspect of the present invention.

If the CPU sets the comparison value, rewriting the comparison value takes, for example, about 10 μsec. However, there is no problem because it takes about 250 μsec to 300 μsec from the start of light emission to the peak position. This is a practically feasible method. Further, it is desirable that the amount of change in the comparison value is the largest for the initial correction amount, and the correction amount is gradually reduced each time it is updated.

FIGS. 13A and 13B are diagrams showing an example of a temporal change in the amount of light emitted from the strobe and a temporal change in the comparison value. However, when the CPU rewrites the comparison value, the output becomes momentarily indefinite, and the digital comparator may output a coincidence signal by mistake and generate a light emission stop signal. Therefore, a circuit device that invalidates such a customary matching signal may be required.

When two or more output pulses are generated during the rewriting of the comparison value from the circuit of FIG.
The count value of 0 may exceed the new comparison value. In this case, the digital comparator 11 further counts up without outputting a coincidence signal. To avoid this count-up, the following may be performed. That is, the increase value of the comparison value is set to be larger than the increase value of the count generated during the rewriting of the comparison value. Alternatively, the CPU reads the count value of the counter 10 after rewriting the comparison value. And CPU
When the count value is larger than the rewritten comparison value and no emission stop signal is output, the emission stop signal is forcibly output. Furthermore, there is a method in which the comparison value is updated by hardware, and the speed of increment of the comparison value is made programmable.

As a matter relating to the dynamic updating of the comparison value, a method of compensating for the bias current of the input terminal of the comparator CMP will be described. Also, the current from the latch-preventing high resistance Rpd and the leak current of the photodiode PD of FIGS. 1, 3 and 6 have the same effect as the bias current of the input terminal of the comparator CMP. I will compensate.

As described above, since the bias current is added to the current of the photodiode PD from the input terminal of the comparator CMP, the capacitor Cpd is charged. for that reason,
Sometimes the comparator CMP is inverted to Hi and the NAND circuit N
AND outputs a pulse. To compensate for this,
The comparison value input to the digital comparator 11 shown in FIG. 6 may be increased with time corresponding to the bias current.

The bias current needs to be measured before the strobe light is emitted. The bias current includes a photocurrent output from the photodiode PD in a normal lighting state. These currents are currents that do not depend on strobe light emission, regardless of the cause. Therefore,
Using the circuit shown in FIG. 6, the number of pulses for each predetermined time is measured before the strobe light is emitted, and the increasing speed is checked. Then, after the strobe light is emitted, the comparison value is corrected and updated by the increase with time. The correction of the comparison value can be performed simultaneously with the update of the comparison value for the above-described brightening correction.

Third, a method using preliminary photometry will be described. This corresponds to the invention described in claim 11. As shown in FIGS. 7 and 8, if the number of full emission pulses is known in advance from the aperture value and the ISO value, the number of stop pulses is determined. When the number of stop pulses is known, the timing at which the light emission stop signal is output can be substantially understood, and the amount of increase in light or the correction amount (correction pulse number) of the bias current can be determined before light emission.

For this reason, before the main light emission in which the strobe emits light in synchronization with the film exposure, for example, about one-tenth of full light emission is performed as preliminary light emission. The amount of reflected light by this preliminary light emission is measured as the number of output pulses using the circuit shown in FIG. 1, FIG. 3, or FIG. The number of pulses in full light emission is estimated based on the measured number of pulses in preliminary light emission.

If the light quantity of the preliminary light emission is sufficiently small, its value does not matter much. However, the light quantity ratio between the preliminary light emission and the full light emission needs to be known relatively accurately.
In order to realize the minute light emission as the preliminary light emission, the strobe is controlled so as to permit the light emission for a predetermined time (for example, about 20 μs). That is, the minute light emission as the preliminary light emission
This is realized by controlling the light emission time.

The ratio between the amount of minute light emission and the amount of full light emission can be checked by experiment in advance. The luminous energy is charged in a large-capacity capacitor called a main capacitor, and if the charging voltage is different, the amount of luminescence changes even during luminescence for a fixed minute time. Normally, the main capacitor is charged to a predetermined voltage, and then the flash is fired to shoot. But,
When shooting is performed continuously, shooting may be performed without waiting for sufficient charging. In this case, the preliminary light emission amount and the full light emission amount are both lower than when fully charged, and the light amount ratio between the preliminary light emission amount and the full light emission amount also changes. If this ratio changes significantly, the ratio of the light emission amount can be predicted by checking the charging voltage of the main capacitor.

FIG. 14 is a diagram showing an example of a time chart in the case of performing preliminary light emission. In the figure, 1 indicates a light emission waveform of preliminary light emission, and 2 indicates a light emission waveform of main light emission. The preliminary light emission is performed with a very small amount of light so that the guide number of the strobe light is not set to a very small value.

In FIG. 14, F indicates the traveling of the front curtain of the shutter, and B indicates the traveling of the rear curtain of the shutter. Also, T
“o” indicates a fully open time of the shutter, that is, a period during which the entire surface of the film is exposed. When preliminary light emission is performed, the number of full light emission pulses can be roughly estimated. Therefore, a method of changing the magnitude of the constant current according to the predicted number of full light emission pulses to improve the dimming accuracy will be described.

In the examples of FIGS. 7 and 8, the number of full light emission pulses was 10,000. This is because, as described above, when the flash is fired at the closest shooting distance of 0.5 m,
This is determined so that the circuit of the capacitor Cpd does not overflow even at the peak of the photocurrent of the photodiode PD. The ratio between the number of full light emission pulses in the preliminary light emission and the number of full light emission pulses in the closest shooting distance corresponds to the decay rate of the peak current between the preliminary light emission and the light emission in the closest shooting distance.
Therefore, if the constant current is reduced based on the decay rate, the number of full light emission pulses becomes the same as the number of full light emission pulses at the closest shooting distance.

In terms of the circuit, it is preferable that the current ratio between the photocurrent at the time of preliminary light emission and the photocurrent at the time of main light emission be selected as an integer. The reason is that it is easy to select the current ratio as an integer from the viewpoint of designing the IC. Making the current ratio an exponential series of 2 is a good method for covering the dynamic range. In addition, selecting an appropriate constant current from a plurality of constant current options has a great effect on dimming accuracy in practical use as compared with the case where only one type of constant current is used. When the constant current is changed in accordance with the aperture value, the constant current can be used in common from the plurality of constant current options.

However, the preliminary light emission needs to be performed immediately before the shutter opening. Therefore, the strobe and the camera need to synchronize the shooting sequence. Many recent cameras communicate with a strobe. Therefore, the camera transmits a timing signal for permitting the strobe to start the preliminary light emission. On the other hand, the strobe transmits a shutter travel permission signal for causing the camera to wait for the shutter to travel until the end of the preliminary light emission. It is necessary to confirm by communication that both the camera and the strobe correspond to the preliminary light emission in the automatic light control mode before the release is started.

FIG. 15 is a flowchart showing the outline of the control on the camera side of the automatic light control by the preliminary light emission. FIG. 16 is a flowchart showing an outline of control on the strobe side of automatic light control by the preliminary light emission. Hereinafter, the procedure of the preliminary light emission and the main light emission will be described based on the flowcharts shown in FIGS.

As is clear from step S1 shown in FIG. 15 and step S101 shown in FIG.
And the strobe CPU periodically communicate as routine work. In step S2, the CPU of the camera performs communication with the strobe and checks whether or not the strobe is of a type that performs communication with the camera. If it is determined that the camera is of the communication type, the camera CPU proceeds to step S3.
Proceed to.

In step S3, the CPU of the camera
Checks whether or not the flash is compatible with a pre-flash synchronization signal in automatic light control photography. If it is determined in step S2 that the strobe is not of a type that performs communication, and if it is determined in step S3 that the strobe is not compatible with pre-flash, in step S5, the CPU of the camera uses a non-pre-flash strobe. The fact is stored in a flag.

If it is determined in step S2 that the strobe is of a type for performing communication, and if it is determined in step S3 that the strobe is compatible with pre-flash, the CPU of the camera determines in step S4 that the strobe is compatible with pre-flash. The fact that pre-emission is supported is stored in a flag. The flash CPU performs the same operations as steps S1 to S5 on the camera side in steps S1O1 to S105. That is, in step S102, the strobe CPU checks whether the camera is of a type that communicates with the strobe. Step S10
In step 3, the CPU of the strobe further checks whether or not the camera requests a synchronization signal for pre-flash in automatic light control photography. If the camera supports pre-flash, the flash CPU stores that fact in a flag in step S104. Also, the strobe CPU is
If the camera does not support pre-flash, step S1
At 05, this is stored in a flag.

There are various types of strobe light control modes in addition to the automatic light control mode. Which type of light control mode is selected is usually determined by the setting of the operation member on the strobe side. Therefore, step S
In the handshake between the camera and the strobe in step 1 and step S101, the following communication is performed. The flash CPU transmits the communication data to the camera, including "automatic flash photography mode" and "requesting a pre-flash synchronization signal". On the other hand, the CPU of the camera returns to the strobe side a message stating that "it is understood that a pre-flash synchronization signal is output in the automatic light control mode". When the handshake is not established,
The flash unit cannot execute automatic light control using pre-flash. In this case, the strobe uses a method of selecting an appropriate constant current according to the aperture value.

In step S6 shown in FIG. 15, the camera checks the start of the release. The release is usually
It starts by pressing the release button of the camera. The camera CPU transmits the start of the release to the strobe (not shown). In step S106 shown in FIG. 16, the strobe detects "start of release" from the camera.

At step S107 shown in FIG.
The strobe CPU refers to the flag set in steps S104 and S105 to determine whether the camera is a pre-flash compatible camera. If the strobe CPU determines that the camera is a pre-flash compatible camera, in step S108,
It is determined whether a pre-flash permission timing signal has been received from the camera. If the strobe CPU has not received the timing signal, it repeats the determination in step S108 until it receives it. If it is determined in step S107 that the camera is not a pre-emission compatible camera, the process proceeds to step S111.

In step S7 shown in FIG. 15, after the camera and the strobe recognize the start of the release sequence, the CPU of the camera raises the main mirror and narrows down the lens. When these processes are completed, the camera can operate the shutter to perform film exposure. In step S8, if the CPU of the camera determines that the strobe is a non-pre-flash strobe by referring to the flags of steps S4 and S5, it immediately proceeds to step S1.
Go to 0. If it is determined in step S8 that pre-emission is to be performed, the process proceeds to step S9.

In step S9, the CPU of the camera transmits a timing signal for permitting preliminary light emission to the strobe.
The strobe CPU detects the timing signal in step S108 shown in FIG. 16, and in step S109, performs preliminary light emission with a small amount of light. The strobe selects a constant current to be used in the main light emission based on the measurement result of the reflected light by the preliminary light emission.

In step S110, the flash C
The PU outputs a shutter release permission signal to the camera after the end of the pre-flash of the strobe. In step S9 shown in FIG. 15, the CPU of the camera receives the shutter release permission signal, drives the rear leading shutter, and starts exposure. Subsequently, in step S11, control of traveling of the first curtain and the second curtain of the shutter is executed.

The time required for the preliminary light emission is short, and the running of the front curtain may be started after a lapse of a predetermined time from step S9. In this case, steps S110 and S10 become unnecessary. In this case, step S1
Instead of 0, a delay of a predetermined time is required. With the above, the control of the preliminary light emission of the strobe is completed. When the front curtain has completed running, the CPU of the camera outputs a synchronization signal from the X contact to notify the timing of the main emission of the strobe. This signal is directly input to the strobe.

In step S111 of FIG. 16, the strobe CPU immediately starts the main light emission upon detecting the synchronization signal, and the strobe CPU controls the amount of light emission in step S112. After the shutter time has elapsed, the camera drives the rear curtain. Note that the control of the traveling of the front curtain and the rear curtain of the shutter is collectively shown in FIG.
As shown.

Thereafter, the camera winds up the film, completes all photographing sequences, and returns to step S1. In step S113, the strobe also detects completion of the winding, and returns to step S101. FIG. 17 is a diagram in which the constant current source CS1 shown in FIGS. 1 and 6 is realized using a current mirror circuit. In FIG. 17, the constant voltage circuit REG supplies a constant current to the collector of the transistor Tr1 via the resistor R. The transistors Tr2 to Tr5 draw currents from the respective collectors according to the respective emitter areas according to the voltage generated at the base and the emitter of the transistor Tr1. The base area ratio of the transistors Tr2 to Tr5 to the emitter area of the transistor Tr1 is equal to the transistor Tr1.
It is the ratio of the emitter current to the emitter current of 1 (≒ collector current).

In FIG. 17, the emitter area of the transistor Tr1 is represented as 1 s, and each of the transistors Tr2 to Tr
The area of the emitter of No. 5 is represented as 1 s to 4 s. k
oreha, means: That is, the transistor Tr2 has the same emitter current as the transistor Tr1,
The transistor Tr3 draws twice the emitter current of the transistor Tr1, the transistor Tr3 draws four times the emitter current of the transistor Tr1, and the transistor Tr4 draws eight times the emitter current of the transistor Tr1.

The transistor Tr6 is different from the transistor Tr
1 to supply a base current to Tr5. The multiplexer MPX selects one of the four transistor output currents based on an instruction of a selection signal from a CPU (not shown) on the strobe side. The selected constant current is used, for example, as the constant current in FIG. The collectors of the other transistors not selected by the multiplexer MPX are connected to the circuit power supply voltage Vcc. Also, in FIG. 17, the current Isink in FIG. 3 indicates the current discharged from the capacitor Cpd and input to the constant current source CS1.

As is clear from the above description, the following effects can be obtained according to each of the above embodiments.
First, since the number of times of discharge of the capacitor Cpd and the amount of discharge charge can be made proportional, the dimming control of the strobe can be performed accurately. Second, since the reverse bias voltage of the photodiode PD can be stabilized and constant current discharge can be realized from the capacitor Cpd, strobe dimming control that is less affected by the circuit power supply voltage can be realized.

Third, in the so-called automatic light control mode in which the strobe light emission is detected by a photodiode provided on the strobe side and a light emission stop signal is generated from the ISO value and the aperture value, the following effects are particularly obtained. Can be. (A) The constant current for discharging the photocurrent is determined by the photographing aperture value and the ISO.
By changing the sensitivity according to the sensitivity, the dimming accuracy can be improved.

(B) The amount of light emission of the strobe is detected as a digital value in real time, and a comparison value compared with the digital value is changed stepwise from the start of light emission, so that the timing of outputting the light emission stop signal is determined. It becomes possible to adjust. Therefore, it is possible to reduce the influence of the error called the brightening.

(C) At the time of photographing, a predetermined minute amount of light is performed immediately before film exposure, the reflected light is measured, and a predicted value of a detection pulse in the case of full emission is estimated from the measured value. By changing the constant current at which the photocurrent is discharged, the accuracy of the dimming control can be improved.

[0127]

According to the circuit for digitizing the amount of received strobe light according to the first aspect of the present invention, the measurement accuracy of the amount of emitted strobe light, that is, the photocurrent can be greatly improved.

According to the circuit for digitizing the amount of received strobe light, the accuracy of measuring the amount of emitted strobe light and the photocurrent can be greatly improved. Specifically, the number of pulses output from the received light amount output means can accurately indicate the amount of strobe light received. According to the circuit for digitizing the amount of received strobe light according to the third aspect, since one discharge is always performed by one transient phenomenon, an error of constant current discharge due to overlapping of transient phenomena can be reliably removed.

According to the electronic circuit for digitizing the amount of received strobe light, the constant current can be adjusted to an appropriate value in accordance with the aperture value and the film sensitivity. According to the circuit for digitizing the amount of received light of a strobe according to the fifth aspect, the constant current can be easily adjusted according to the aperture value of the camera and the film sensitivity.

According to the circuit for digitizing the amount of received strobe light according to the sixth aspect, it is not necessary to take any special measures on the circuit.
According to the strobe light receiving amount digitizing circuit, it is possible to effectively prevent the measurement accuracy of the strobe light emission amount (photocurrent) and the deterioration of the strobe light control accuracy due to the fluctuation of the power supply voltage. Can be.

According to the strobe light emission amount control circuit, the measurement accuracy of the strobe light emission amount, that is, the photocurrent can be greatly improved. Also, the number of pulses output from the received light amount output means can accurately indicate the amount of strobe light received. Furthermore, high accuracy can be obtained with respect to dimming control for stopping strobe light emission during light emission.

According to the strobe light emission amount control circuit of the ninth, tenth, and eleventh aspects, it is possible to reduce the influence of an error called brightening in which light emission continues after the light emission stop signal is output. According to the flash light emission amount control circuit of the twelfth aspect, since the plurality of current values are exponential series of powers of two, it is easy to implement an IC and can cover a dynamic range of a plurality of constant currents. it can.

According to the flash light emission amount control circuit of the thirteenth aspect, the flash light control can be accurately performed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a strobe light receiving amount digitizing circuit according to the present invention.

FIG. 2 is a time chart showing the operation of the first embodiment shown in FIG.

FIG. 3 is a circuit diagram showing a second embodiment of a strobe light receiving amount digitizing circuit according to the present invention.

FIG. 4 is a diagram showing a full emission waveform of a general strobe.

FIG. 5 is a diagram showing a light emission waveform when a peak current is reduced.

FIG. 6 is a circuit diagram showing a first embodiment of a strobe light emission amount control circuit for generating a light emission stop signal by using the strobe light reception amount digitizing circuit shown in FIG. 1;

FIG. 7 is a diagram showing the relationship between the number of stop pulses and the number of full emission pulses at each ISO value, each aperture value, and each distance.

FIG. 8 is a diagram showing the relationship between the number of stop pulses and the number of full emission pulses at each ISO value, each aperture value, and each distance.

FIGS. 9A and 9B are diagrams showing the amounts of light received by a photodiode PD when the same amount of strobe light is irradiated on a subject at a short distance and a subject at a long distance. .

FIGS. 10A and 10B are diagrams showing a relationship between a light receiving amount of a photodiode and time, and particularly show a state from when a light emission stop signal is output to when light emission is stopped.

FIG. 11 is a diagram showing the relationship between the number of stop pulses and the number of full emission pulses at each ISO value, each aperture value, each distance, and each constant current ratio.

FIG. 12 is a diagram showing the relationship between the number of stop pulses and the number of full emission pulses at each ISO value, each aperture value, each distance, and each constant current ratio.

FIGS. 13A and 13B are diagrams illustrating an example of a temporal change of a light emission amount of a strobe and a temporal change of a comparison value.

FIG. 14 is a diagram illustrating an example of a time chart when performing preliminary light emission.

FIG. 15 is a flowchart showing an outline of control on the camera side of automatic light adjustment by preliminary light emission.

FIG. 16 is a flowchart showing an outline of control on the strobe side of automatic light control by preliminary light emission.

FIG. 17 is a diagram showing a constant current circuit realized using a current mirror circuit.

FIG. 18 is a circuit diagram showing a first example of the related art.

FIG. 19 is a circuit diagram showing a second example of the related art.

[Explanation of symbols]

BA power supply Cpd Capacitor CMP comparator CS1 Constant current source CK Sample clock Cc Capacitor Dc Diode D2 Two diodes connected in series D3 Three diodes connected in series D4 Four diodes connected in series FF D flip-flop Isink Discharge current from capacitor Cpd PD Photodiode MPX Multiplexer NAND NAND circuit Rpd Latch prevention resistor Rc resistor R1, R2, RL resistor REG Constant voltage circuit RT Variable resistor Tr1, Tr2, Tr3, Tr4, Tr5, tr1, t
r2, tr3, tr4, tr5, tr6 Transistor Vcc circuit power supply voltage

Claims (13)

[Claims] 1. A photoelectric conversion unit that receives light from a strobe and generates an output according to the intensity of the received light, a storage unit that stores an output generated by the photoelectric conversion unit, and a storage amount of the storage unit. When exceeds a predetermined threshold value, in synchronism with a predetermined sampling frequency, and during a predetermined period shorter than the sampling period, a predetermined storage amount is released from the storage means, and the storage amount of the storage means is A constant-amount discharge unit that performs feedback control to maintain the accumulation amount of the accumulation unit near a constant value; and a light-receiving amount output unit that outputs a pulse signal when the accumulation amount of the accumulation unit exceeds a predetermined threshold. And a strobe light receiving amount digitizing circuit. 2. A photoelectric conversion means for receiving light from a strobe and outputting a current corresponding to the intensity of the received light, and a current / voltage for accumulating a current output from the photoelectric conversion means and converting the current into a voltage value. Conversion means, when the voltage value output from the current / voltage conversion means exceeds a predetermined threshold, synchronizes with a predetermined sampling frequency, and in a predetermined period shorter than the sampling cycle, Constant current discharging means for discharging a constant current from the voltage conversion means, feedback-controlling the output voltage of the current / voltage conversion means, and maintaining a voltage value output from the current / voltage conversion means near a constant voltage; -When the voltage value output from the voltage conversion means exceeds a predetermined threshold value, the light reception amount output means outputs a pulse signal. Digitizing circuit for strobe light reception. 3. A strobe light receiving amount digitizing circuit according to claim 2, wherein the constant current discharge from said current / voltage conversion means is performed over a half cycle of said sampling cycle. Quantity digitizing circuit. 4. The circuit according to claim 2, wherein the constant current changes according to an aperture value of the camera and a film sensitivity. 5. The strobe light receiving amount digitizing circuit according to claim 4, wherein the constant current that changes according to an aperture value of the camera and film sensitivity is selected from a plurality of predetermined current values. Digitizing circuit for strobe light reception. 6. The strobe light receiving amount digitizing circuit according to claim 5, wherein a plurality of current values specific to a manufactured circuit are used as the plurality of current values. 7. The strobe light receiving amount digitizing circuit according to claim 2, further comprising: means for stabilizing a reverse bias voltage of the photoelectric conversion means, and means for preventing the threshold from being affected by a power supply voltage. 3. A circuit for digitizing the amount of received strobe light according to claim 2. 8. A photoelectric conversion means for receiving light from the strobe and outputting a current corresponding to the intensity of the received light, and a current / voltage for accumulating the current output from the photoelectric conversion means and converting the current into a voltage value. Conversion means, when the voltage value output from the current / voltage conversion means exceeds a predetermined threshold, synchronizes with a predetermined sampling frequency, and in a predetermined period shorter than the sampling cycle, Constant current discharging means for discharging a constant current from the voltage converting means, feedback controlling the output voltage of the current / voltage converting means, and maintaining a voltage value output from the current / voltage converting means near a constant value; If the voltage value output from the voltage conversion means exceeds a predetermined threshold, the light reception amount output means that outputs a pulse signal, and counts the pulse signal, If the serial count value exceeds the comparison value predetermined amount of flash light emission control circuit, characterized in that it is composed of a flash light emission stop means for outputting a light emission stop signal to the flash. 9. The strobe light emission amount control circuit according to claim 8, wherein the comparison value is set to a value smaller than a design comparison value determined by an aperture value and a shooting distance. circuit. 10. The strobe light emission amount control circuit according to claim 9, wherein the comparison value changes stepwise as time elapses after the start of strobe light emission. . 11. The strobe light emission amount control circuit according to claim 8, wherein the strobe light emission stopping means counts the number of the pulse signals based on a small amount of light emission performed by the strobe, and based on the count result, A strobe light emission amount control circuit, wherein the constant current at the time of main light emission following a minute light amount is selected from a plurality of predetermined current values. 12. The strobe light emission amount control circuit according to claim 11, wherein the plurality of predetermined current values are an exponential series of powers of two. 13. The strobe light emission amount control circuit according to claim 11, wherein a difference between the predetermined plurality of current values and a plurality of current values realized by an actual circuit is stored in a nonvolatile memory. A strobe light emission control circuit, comprising: a memory storage unit that performs the correction; and a correction unit that corrects the predetermined comparison value based on a difference between the current values stored in the memory.